scala multiple inheritance

Here, we are representing all types of inheritance by using pictorial form.

Had Scala supported multiple inheritance, the above calls would have created an ambiguity as one cannot be sure which of the print functions would get called, or even whether the print function of the base class would get called thrice.

Scala supports various types of inheritance including single, multilevel, multiple, and hybrid. The compiler detects diamond occurrences, and fires an error if a function is implemented by multiple parent classes. Developed by JavaTpoint. java methods inheritance interfaces multiple interface button class therefore defines method each Alongsidesimple inheritance, there ismultiple inheritance: C++ is famous for allowing multiple inheritanceand describing thediamond problem. While Scalas approach is more elegant, Kotlins is consistent with its philosophy: being explicit and readable before being concise. The above diagram translates into the following code: Scala resolves the diamond problem by definingone main super trait,whose code will be used, among all super traits. Let us now use the equation to linearize the DerivedClass. Inheritance is one of the basic tenets of Object-Oriented Programming, along with encapsulation and polymorphism. We will use our sample class hierarchy to explain the above linearization equation. But Scala avoids this ambiguity by linearization. But unlike Java Interfaces, Scala traits can actually define any concrete methods. C++ has its own way of coping with the diamond problem. You can use single, multilevel and hierarchal in your class. Yet, interfaces can have concrete functions. Copyright 2011-2021 www.javatpoint.com. Multiple and hybrid can only be achieved by using traits. Over 2 million developers have joined DZone. All rights reserved. a class which extends class is called derived or base class. A class which is extended called super or parent class. So the final linear form of the DerivedClass is: (DerivedClass, Trait3, Trait2, Trait1, BaseClass, scala.AnyRef, scala.Any). Thus the linearization equation of BaseClass would be, (NOTE: Though we did not add any super class of BaseClass, as per Scala hierarchy the default super class of any Scala class is scala.AnyRef, similarly scala.AnyRef extends scala.Any). If we call the print function of the DerivedClass we will get the following output: This proves that when we call the print function of the DerivedClass, since each of the classes/traits has a call to super.print, the call will follow the above linear sequence and thus Scala avoids multiple inheritance. Opinions expressed by DZone contributors are their own.

Scala doesnt allow for multiple inheritanceper se, but allows us to extend multiple traits. The main one is set with theextendskeyword, while the others are setwithwith. It states that theres an issue when a child class inherits from multiple classes that have the same method. In order to avoid it, Java completely disallows multiple-inheritance. Published at DZone with permission of Nicolas Frnkel, DZone MVB. and then apply the above series of equations, we will get a different linear form of our DerivedClass which will be: So, the conclusion is that the definition of a trait does not define the linear form, instead how it is mixed-in with a class defines the actual linear form. For example if we change the definition of our DerivedClass from. JavaTpoint offers too many high quality services. Inheritance is an object oriented concept which is used to reusability of code. You can achieve inheritance by using extends keyword. From this it seems apparently that Scala supports multiple inheritance; but that is not the case.

To fix this, the developer must explicitly code the desired behavior. Join the DZone community and get the full member experience.

To illustrate this linearization technique we will use some Scala classes mixed-in with Scala Traits as shown in the inheritance structure below: Now, say, BaseClass has a function print and each of the traits as well as the DerivedClass overrides the print function and also calls the print function of the super class. If we want to find out the linearization structure of DerivedClass defined as. So the class/trait definitions are as follows: So the question is, if we call the print function of the DerivedClass what will be the call flow of the print function of the super classes. JavaTpoint offers college campus training on Core Java, Advance Java, .Net, Android, Hadoop, PHP, Web Technology and Python. If we simplify the above equation and apply the `+:` operation we get the following equation: Just to explain the above simplification logic we are using the +: operation which is defined as, the BaseClass, scala.AnyRef, scala.Any of the left operand is removed since the right operand also has the same and the result is. then the above parameters of linearization for this DerivedClass would be: And then the linearization equation for the DerivedClass will be: Now we will apply the same equation for all other classes and traits. Of course, nothing prevents us from overriding the method. See the original article here. (Please note that each of the overridden function in each class/trait has a call to the print function of the super class). To achieve inheritance a class must extend to other class. To avoid multiple inheritance Scala uses a technique called linearization to flatten calls to super classes. To support inheritance Scala has introduced a concept called trait, almost similar to Java Interfaces. Applying the same equation for Trait1 which is defined as: So we get the following linear form of all the classes/traits: Except for the DerivedClass all other classes/traits have the linear form. The following diagram shows the inheritance and the linearization for our sample classes/traits: The linear form of a class hierarchy will depend on the order of the traits imported. Mail us on [emailprotected], to get more information about given services. Hence, in the above example,WindowDoor.open()will, by default, use code fromDoor.open(). The following is the code above translated in Kotlin: Kotlin takes another path to solve the diamond problem: explicit overriding. Inheritance (object-oriented programming), Scala vs. Kotlin: Multiple Inheritance and the Diamond Problem, Benchmarking PostgreSQL Workloads on Kubernetes.

As in Scala, Kotlin doesnt allow us to extend multiple super classes. Scala Linearization technique uses the following equation to flatten the calls to the super classes and avoid multiple inheritance (Reference Scala Language Specification Section 5.1.2): Where +: denotes a concatenation function where elements at right hand operand replace identical elements of the left hand operand as follows: Also C1 Cn denotes the inherited classes/traits in the order that they are declared for the class from left to right. Lets check how Scala and Kotlin fare. Please mail your requirement at [emailprotected] Duration: 1 week to 2 week.

scala multiple inheritance

scala multiple inheritanceLeave a Comment melissa and doug furniture dollhouse

scala multiple inheritance
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